Routine electrocardiogram (ECG) monitoring is standard practice in coronary and intensive care units, emergency rooms, ambulatory monitoring settings and operating rooms. Frequently, continuous ST segment monitoring is carried out in order to detect ST changes which may indicate ischemic episodes. Data obtained from such a monitoring are automatically displayed on a monitor to show a clinician the status of the patient. For carrying out an ECG test, a variable number of ECG electrodes are positioned on a patient in a way that the electrodes form a predefined arrangement, e.g. accordingly to “Einthoven”, “Goldberger” and “Wilson”, EASI, “Frank” or others. A standard 12-lead ECG may have, for example, six vertical leads of a 12-lead-ECG, namely aVF, III, aVL, I, aVR and II (clockwise). Thereby the bipolar “Einthoven” leads I, II and III and the unipolar “Goldberger” leads aVR, aVL and aVF are used. The displayed values can be obtained from a mathematical linear combination of the values of the electrical voltages obtained from the ECG electrodes. The position of the axes in the displayed image and their angles represent the location of its corresponding ECG electrodes on the patient's body during the ECG test.
Likewise, six axes relating to the six horizontal “Wilson” leads of a 12-lead-ECG, namely V1, V2, . . . V6 are used. Again the position of these axes and their angles represent the location of its corresponding ECG electrode on the patient's body during the ECG test. Not all the leads need to be measured, as some of the leads can be derived from a linear combination of other leads.
One of the clinically important uses of the ECG is to detect acute myocardial infarction and indicate the location and even the extent of the jeopardized myocardium, because acute transmural ischemia caused by occlusion of a major coronary artery produces an epicardial injury current that can be detected as a deviation of the ST segment toward the involved region. Depending on the degree of the ischemic event, the ECG will show an ST depression (negative voltage) or an ST elevation (positive voltage). For the left anterior descending coronary artery, this typically appears as ST elevation maximal in precordial leads V2 or V3, and for the right coronary artery, as ST elevation maximal in limb leads aVF or III. However, except when the left circumflex coronary artery is dominant (supplies the posterior descending artery), its acute occlusion is represented instead by ST depression maximal in leads V2 or V3. The elevation or depression of the ST segment in a particular lead combination will point to the particular area of the heart that experiences an ischemic event.
The method of ECG display can enhance or obscure the diagnostic information needed to support the therapeutic decisions made for patients with acute coronary syndromes. The classic display includes two segregated groups of the six limb leads (I, II, and III; and aVR, aVL, and aVF) and two integrated groups of the six precordial leads. The limb leads are typically regrouped into a single orderly sequence, which includes locating inverted aVR (−aVR) between leads I and II to create an integrated logical display of cardiac electrical activity in the frontal plane, similar to that used in the classic display for the precordial leads. With these displays, the zero voltage ST-segment deviation is then located at the center of the display, which makes allocation of the direction of ST-segment deviation to localize the site of acute coronary syndrome difficult.
Accordingly, there is a need for an improved display format for the limb leads and the precordial leads which improves the clinical value of a standard ECG, for example, for the detection of myocardial infarction and the evaluation of intra- and post-operative ischemia.